1. Field of the Invention
The present invention relates to a technique of detecting an acceleration when the orientation of an object changes and executing a function of a device in accordance with the detected acceleration.
2. Description of the Related Art
An example of a conventional acceleration detection apparatus includes an acceleration sensor using, for example, means for detecting a change in the electrostatic capacity generated between a movable electrode and a fixed electrode of a sensor based on an acceleration added to an object. In recent years, a three-axis acceleration sensor capable of detecting an acceleration added in any direction of a three-dimensional space by one sensor has been developed. The three-axis acceleration sensor is mounted on a compact digital camera, a cell phone, etc. and can detect a gravity acceleration in the direction of gravitational force when the device is still to detect the orientation and movement of the device. The characteristic that the acceleration in the axis direction, in which the acceleration is generated, changes when the user picks up the device or intentionally shakes the device is used to determine the change in the orientation and movement of the device and the intentional shaking movement. The three-axis acceleration sensor is applied to input means for changing a displayed image or executing an enlargement or reduction function in accordance with the determined orientation and movement of the device or to shake prevention control means for preventing hand shake of camera, etc.
For example, Japanese Patent Laid-Open No. 2002-296663 describes using a three-axis acceleration sensor to detect the orientation of the camera, changing the projection position of date data, etc., and preventing the shutter movement if the acceleration generated by the hand shake is equal to or greater than a predetermined value. Japanese Patent Laid-Open No. 2002-049067 describes a shake prevention function of using a plurality of acceleration sensors to correct a rotational vibration.
However, when the acceleration sensor is used as input means for executing a predetermined function in accordance with an intentional shaking movement of the user, an acceleration generated by an unintended movement of the user, such as putting down the device on a desk or picking up the device, may be detected, and the sensor may be erroneously operated. Furthermore, when a shaking movement in the up and down direction and back and forth direction is determined to change functions allocated to the directions, one axis with the maximum acceleration is detected to decide the shaking direction. However, a shaking direction different from the user's intention may be falsely detected in the method.